Colon polyps and neoplasmsDownloads

A 62-year-old man comes to the physician because of progressive fatigue and dyspnea on exertion for 3 months. During this time, he has also had increased straining during defecation and a 10-kg (22-lb) weight loss. He has no personal or family history of serious medical illness. Physical examination shows conjunctival pallor. Laboratory studies show microcytic anemia. Test of the stool for occult blood is positive. Colonoscopy shows an exophytic mass in the ascending colon. Pathologic examination of the mass shows a well-differentiated adenocarcinoma. A gain-of-function mutation in which of the following genes is most likely involved in the pathogenesis of this patient's condition?

A 19-year-old man comes to the physician because of a 2-day history of blood-speckled stools and a protruding rectal mass. He has no abdominal pain, altered bowel habits, or fever. His mother has inflammatory bowel disease. His vital signs are within normal limits. Examination shows multiple, small, hyperpigmented maculae on the lips, buccal mucosa, palms, and soles. The abdomen is soft with no organomegaly. Rectal examination shows a 4-cm pedunculated polyp with superficial excoriations on the mucosa. A colonoscopy shows 14 polyps. A biopsy shows hamartomatous mucosal polyps. This patient's diagnosis is most likely?